The primary objective of this Phase I study is to assess the safety & efficacy of recombinant factor IX (rhFIX) administered by intravenous infusion in patients with severe hemophilia B. Secondary objectives are: to estimate the pharmacokinetic parameters, including recovery and half- life, of rhFIX administered as an IV infusion during the first segment of the study; to evaluate the pharmacokinetic parameters, including half-life and recovery of rhFIX and Mononine during the first segment of the study.